Mine timber



I June 6, 1950 M. J. MECHLING MINE TIMBER 2 Sheets-Sheet 1 Filed Oct. 25, 1946 IN VEN TOR. Mo/vzoe J. Mac/l4 we J 1950 M. J. MECHLING 2,510,593

MINE TIMBER 2 Sheets-Sheet 2 Filed Oct. 25, 1494 K \XTTW'TYY m NVTUVTOR.

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Patented June 6, 1950 UNITED STAT ES PATENT OFFICE MINE TIMBER;

Mcnroe Livreemin Greensburg, Pal

Application October .25, 1946, Serial No. 705,605

15 Ciaiiiisl.

This invention relates: to. mine timbers and, more particularly, to prefabricated mine timbers for supporting the roofs of undergroundentries, passageways. excavations. or tunnels hereinafter referred to as shafts.-

The object of this invention is the provision of a new and improved mine timber which is simple in structure, physically strong, easily and simply installed, and adjustable both in width and height for adaptation to a maximum. number of variable conditions.

Another object of this invention isthe provision of a new and novel mine timber for supporting the roofs of underground shafts/which utilizes the lateral stability of the walls vof the shaft for supporting the roof and maintains the floor of the shaft free from the usual roof supporting obstructions;

' Another object is the provision .of .anew and novelmine timber for supporting the roofs of underground shafts which has articulatedmen'ibers for supporting the roof, the membershavifng relatively large interengaging load transferring surfaces whereby the danger of failure of the articulated joint is lessened.

A further object isthe provision of a new and improved mine timber of the type referred to having adjusting. .means for facilitating Dositioning of the timber for obtaining an initial supporting action.

Still another object, is the provisionof anew and novel supporting means for .the roofs of underground shafts which ,is. self-adjusting for shafts of different widths.

Still another object of this invention is the provision ofa newand improved load transferring joint for articulated members comprising means for maintainin the members in assembled relationship, and mating surfaces for transferring the load from one member to theflotherlindependently of the means for maintaining .the members assembled.

The invention resides in certain constructions and combinations and arrangements vofparts,v and further objects and advantages will be apparent to thoseskilledin the art to whichit relates from the following description of the preferred em! bodiment described with reference to the ac.- companying drawings forming a .part of this specification, and in which:

Fig. 1 shows a cross-sectionalview of amine shaft having installed therein a 'mine timber embodying the presentinvention;

Fig. 2 is an enlarged perspective-view of a'portion of the timber;

Fig. .3 is anenlargedside vi'e.w of-a .portionpf the timber;

Fig. 4- is a view similar to Fig. 1 shQW'ing-a modification; 7

gFigas shows another modification;

Fig. 6v is yet another modification;

Fig. 7 is n enlarged re spective' view of a po tidnof the timber shown in Fig. 6; V

Fig. .8' is an enlarged side view of a portion of the timber shown in Fig. 6;

Fig. 9 is an enlarged perspective view of a portion of a modified mine timber;

Fig. 10 is a side' view of the modification shown in Fig. ,9} and t Fig. 11 is a fragmentary view of a section of a mine shaft having mounted therein another modification of a, mine. timber embodying the present vention.

Gener ,l' sp a i the invention comprises a roof or" other overhead structure support which bears at its ends in opposing wallsis fully ad iustable, and t n s. jql nsth n. wh n the; we to e supp ted 1 p lied thereto, u lizi the t a tabili f he walls f in inc ease e u y of up or Whil the inventi n s sc ib wi h a ti l e erence to th Sunnornnsfl th o s ofun e oimd she ric as mine shafts, it will be appreciated that the invention is also applicable to" other uses wherein a maximum of supporting strength is equired with a minimum of weight and materialsjin' the supporting elements.

Referring to the drawings where a nuinber'of embodiments of the invention are shown. Figs. 1, 4,5; 6, and 11 show cross-sectional views of amine shaft A- havingverticalside {walls-t0; l I, a floor 12*, andar'oof l-3-"to besupported, each with a" different roof support or mine "timber B-posfftioned therein in supporting;relations-hip with the roof I3 Intlie embodiments shown, the mine timber B comprises a horizontal roof sup porting member or beam 16 positioned transversely of th'e'shait and substantial parallel relationship with-the roof t3 and relatively short beam supporting members 48;. l 9",.each" articulated atone end to an endzof the .beam I6and'.-ex.-: tending outwardly anddown'wardly on an angle into artificially made niches 21,22 inthe walls i0, :11 respectively where the entire weightwof the roof is borne;

For-:Itransferring the weight .of the roofst'ruc ture h3-to the. mine timber B,-;awejodenbear;n 23 is preferably positioned between the trans,- versecbeam l6; and the roof J13; providing ga wide bearing area for the material .of the roof and '23 throughya bearing plate- .25 suitabl mounted on. thewnpper endiof th jack- ;shaft 2d: 'uch that the platesfi remains stationary while the jack shaft 24 is screwed into supporting engagement with the beam 23. As shown, a pair of blocks 3|, 32 which may be slightly wedgeshaped for facilitating insertion may be positioned intermediate the ends of the supporting member l6 and the ends of the beam 23 for supporting the ends of the beam 23 and relieving some of the weight on the jack shaft at the center of the beam [6. These blocks may be driven into place after the mine timber is otherwise installed and the jack shaft 24 operated so as to transfer the weight on the beam 23 to the supporting member l6 and thence through the supporting members l8, l9 to the Walls H], II.

In the timber shown, articulation of the members l8, l9 relative to the transverse beam is efiects a lengthening or shortening of the overall longitudinal length of the timber B and facilitates installation of the same sized timber in mine shafts of difierent widths. Variations in the over-all vertical height of the timber caused by articulation of the members l8, H5 in compensating for the different widths of the mine shaft may be compensated for by suitable adjustment of the jack shaft 24. In addition, adjustment of the jack shaft 24 provides a compensating means for differences in the height of the niches 2i, 22 from the level of the roof l3 or for different thicknesses of supporting beams 23 or blocks 3|, 32, or both.

As shown, the outer or lower ends of the members l8, 19 may have their upper or outer surfaces cut on a longitudinally diagonal plane providing a sharp edge on that end of the member for engaging in the niches 21, 22 and transferring the weight of the roof on the timber B to the walls H], H. It will be appreciated that this weight can become quite large and impose a considerable supporting burden on all the members, and particularly on the articulated joint between the members l8, l3 and the transverse beam l6. This invention contemplates providing surfaces other than those retaining the members in articulated relationship for bearing this load between the members. In the embodiment of the invention shown, the members I8, 19- are held in articulated assembled relationship with the transverse beam [6 by means of a transverse horizontal pin 34 fixedly mounted in each end of the supporting beam I6 and journalled in suitable holes 35 in the upper or inner end of the supporting members. The pin 34 must of necessity have a diameter somewhat less than the width of the member in which it is mounted or journaled and is not capable of transferring a large amount of weight from the roof supporting member [5 to the depending members l8, l9 due to the relatively small crosssectional areas which can be brought into engagement to transfer this load, the stress here involved being directly proportional to the load and inversely proportional to the diameter of I end of the roof supporting member l6 against which the surfaces of the articulated ends of the depending members l8, I9 respectively may engage, and the diameter of the hole 35 in which the pin 34 is journaled is made sufficiently greater than the diameter of the pin 34 such that the ends of the depending members l8, [9 may engage their respective surfaces when a load is placed on the roof supporting member I6. It is preferable that the angle between the depending members l8, l9 and the roof supporting member l6 be fully variable so as to compensate for different shaft widths and insure that the surfaces always transmit at least the major proportion of the load. Accordingly, these surfaces are made curved and preferably arcuate with a center of curvature approximately coincident with the axis of the pin 34 whereby the members l8, [9 may be articulated through a maximum swing with the surfaces still bearing the major proportion of the load. Alternatively, a ball and socket joint could be provided, although possibly with a slight sacrifice of the lateral stability from that obtainable with the structure shown.

The articulated joint described facilitates manual articulation of the members while the timber is being installed and enables further articulation even when the timber is under relatively heavy loads. Any weight bearing on the members tends to effect a longitudinal lengthening of the timber, which lengthening is resisted by the body of the material forming the wall and its lateral stability whereby the lateral stability of the wall contributes materially to supporting the timber in position and the roof in place. With the structure shown, the Vertical component of the weight of the roof on the timber is directed by virtue of the articulated joint in an angular direction coincident with the axis of the supporting members l8, 19 deep into the walls 10, l l. Any crushing or failure of the walls adjacent the point of insertion of the lower and outermost ends of the members I8, [9 merely serves to make the wall denser at this point and increases its ability to resist the forces on the timber and thus to support the roof l3. While the members l8, l9 may have any relative angle to the horizontal, it is preferred for best results to take advantage of the lateral stability of the walls I0, I! that this angle be somewhere between 30 to 60, although it may be more or less.

The members l6, l8, l9 may be formed in any suitable manner to give the maximum amount of strength for a minimum weight of timber. Thus, in the embodiment shown in Fig. 1, the roof supporting member 16 is an I-beam having top and bottom horizontal flanges 40, 4| joined by an intermediate spacing web 42, while the depending members l8, [9 may be formed from an H-beam having vertical flanges 44, 45 and an intermediate transverse web 46. Whensuch structural shapes are utilized to form the members, the web 42 may extend beyond the flanges 40, 4| at each end of the member l6 and provide a central mounting support for the pin 34. The surfaces 38 may be provided by welding or otherwise securing suitable shaped pieces of metal or other material intermediate the flanges 40, 4! and'on both sides of the web 42. Similarly, other material may be welded between these flanges and on either side of the web adjacent the middle of the member IE to provide a suitable threaded support forthe jack shaft 24 and, if necessary, to provide increased strength at this point. In

this embodiment of the. invention the. beam i5. is la ly longa dthe: cl'encudingv membe s I 8; l-9 re1atively short andsuppoitted in. niches 2' 22,. high on the. wall so. thatthetimber obstructs a minimum rea. of the shaft.

In the embodiment of the invention shown. in Fig. 4. the roof supporting; member 6 relatively short compared to the transverse width f. the'shaft A while thedepending members 18;. i9 are relatively long. and enga e the. walls, at. points further spaced from the. roof than. the. embodiment shown in. Fig. 1. The. member. t5. be. formed from a block. of. solid material suitably cut away at the ends toleave central. vertical webs 5n, 5! in which the pin 34 may be mounted,

while the depending; members may be formed. from an I-beam. Spaced v vertical. flange 52, 53-.

having the enlarged openings for receiving the pin 34 and rounded on their ends for engage. ment against the arcuate surfaces on the beam.

I6 are fixed to one end of the I-beamsand form the articulating. means for the members. [8, l9. Stops 54, may be provided on theupper surface of each depending member l8, l9. having a substantially horizontal surface upon. which blocks, in this instance vertically elongated, may rest-in supporting relationshipbetween the members lfl, l9 and the beam 23.

Fig. 5- shows another modification of the invention wherein the beam l6 has been entirely eliminated and the depending members I8, l9 are articulated relative to each other to iorm the mine timber. In this embodiment of. the invention, the articulated end ofthe member [9 has a central web for mounting the pin 35 and the articulated end of the member l-lhas-spaced vertical plates or flanges with the openings 35, formed therein for looselyiournaling the'pin 34. Abutting arcuatesurfaces having a center ofcurvature substantially aligned with the. pin. 34 for bearing the forces involved independently oi. the pin 34 are provided as shown in thefigure. The member l8, l9 have radial transverse-abun ments; 69. 6| on theirupper suriacewhich limit. the articulating movement of themembers !8,. I 9. in a downward direction, In a similar manner to the embodiment showninFig. 4,.theembodiment shown in. Fig. 5. has suitable stops midway of the length of the members for receiving the supporting blocks 3.! 3.2, which in this embodiment. transfer all the weight of the roof l3. on thebeam 23 to the mine timber.

In the embodiment. of. the. invention shown. in Fig. 6, the point of articulation of the roof sup.- porting, member 16" and the depending members [8, I9 is. adjustable longitudinally of. the beam l6. As shown, the member I6 is a T-beam. with an upper horizontal flange. till and a depending verticalflange or Web 65 having. therein. adjacent its lower edge a longitudinally extending opening '66 with aplurality of notches 61 extending angul'arly upwardly therefrom so as to be inclined toward the center line of the member. The. depending members 18, f9 are of H-beam construction having vertical flanges 10, TI and ahorizontal web 12; therebetween, the web 12 being cut away at the articulated end to provide clearance for the web 65-. In. this embodiment the pin 34v is fixedly mounted adjacent the articulated ends of the members l8, 1-9 in the flanges 10, 1I-, the ends ofwhich are rounded having a center of curvature approximately aligned with the axis of thepin 34. The roof supporting member I6 has a plurality of longitudinally spaced transvers y xtending abutments- 13 depending rrom the lower. surface of. the. flange (i4- om each. side or the web. 65. and. so positioned. that when thepin34 is. in any oneof the slots. 6i. tl'resur-v faces of the abutments will. en a e the rounded v edges. of. the flanges. 1i), 1 I, thus. transmitting. the

load on the beam it to. the. depending. members. [8,- [31 Adjustmentmay be effectedby disengaging the pin 3.4 from, any notchfi'l'andjslidingit in. thelongitudinalopenings 6.6. to any other notch desired, a, different. abutment 13 being provided. for each notch. In this embodiment. of the. in vention, the jackshait 24' is providedpn. its upper endw-ith aconical-suriace for engagingthesupporting beam 231 and providing. asecond adjust.- ment.

Fig. 9 showsanother. modificationof theinvention whereinthe member. I6. isinstheform. of an inverted U-shaped channel having a base 151and. depending flanges or webs 16,. 1.1. Each. flange. has.a.longitudi nally extending opening 18' adjacent the. lower edge. similar to. the opening 6.6}. in. the web65 and with a. plurality of longitudinally. spaced upwardlyv extendingslots 1:9. The. member [.6 has suitable; longitudinally spaced trans-- versely extending abutments between the flanges. 16, 1.1: so. positioned: that. when the pin. is.positioned in any pairof. slots, the rounded end of the member I8 may en age the. adjacent abutment, the widthand epth oi theslots 19, being such. that engagement will occur before the. pin 34 engages. the sides thereof. Thus. in. the. em.- bodiments shown inFi-gs. 6.. to 9,.the. mine, timbers may :beplaced. imposition. andi apoint of articulation. chosen for the. depending members. [8, L relative, to the supporting, member lfif such as will facilitate installation. of the timber and provide. full and safe support for. the roof of the shaft.

In theembodiment of the. invention shown in, Fig. 11, the. dependingmembers l8, [Hare made adius able in le th and as shown comprise a .base. 80' pointedon its lower end. for enga ement in a niche of thewall I'll. a threadedljshaft 83"having on its upper end a member 84 for articulation with the supporting member [6, and a collar. on the base 80 threadably engaged. with the shaft 83, rotation of which either extends or retracts. the, shaft 83 andadjusts the length of the member [8.

To install. the mine timber shown in the figures. the. niches. 2|. 22. are first cut in the' walls, l0. II at a suitable height above the. floor 12,, which height is; not critical. The minev timber is then hoisted substantially: into position with the. jack. shaft 24. screwed down. as far as'it will go, and the lower ends. of the members l8... ['9 are positionedin the niches 2|, 22. The beam 2'3 is positioned above the timber and in substantially parallel relationship with the supporting member IS. 'The supporting member I6 is; then moved longitudinally so as to position it as closely as possible to the" transverse center of the shaft A; and the jack shaft 24 i screwed upwardly until" it forces the beam 23 into firm engagement with the roof 13 of the shaft A, at which time the mine timber is properly in position. When so installed the friction between the plate 25 and the beam 23 prevents further longitudinal movement of the supporting member I6 and holds the mine; timber. securely in position. l he blocks 3 I, 32' may then be installed. Any-weight exerted on the supporting member IB- as a result of the roof 13- ofthe shaft A sagging will be trans-mitted to the depending members it, I9 through a surface of substantial bearing area andthonce aims to the relatively firm and substantial side walls l0, II at an angle such that a substantial component of the weight attempts to push the side walls H], II (laterally. This lateral component, which may be otherwise described as a tendency for the timber to lengthen longitudinally, is resisted by the lateral stability of the side walls whereby the timber may take advantage of this stability for producing a support which is structurally capable of preventing the disastrous caveins so common in mine shafts.

Thus it will be seen that the invention described accomplishes the objects thereof and provides a mine timber which is simply installed, adjustable to mine shafts of different widths, and which tends to lengthen as a result of bearing a weight whereby the lateral stability of the walls of the mine shaft may be utilized for aiding in the support of the roof.

It will be appreciated that modifications and alterations differing materially in appearance and structure will occur to others skilled in the art upon a reading and understanding of this specification, and it is my intention to cover all such modifications and alterations insofar as they are within the scope of the appended claims.

Having thus described my invention, I claim:

1. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a plurality of elongated members loosely pivotally connected together with the free ends of said timber being adapted to be received in niches in opposite side walls of the shaft, the over-all length of said timber being greater than the width of the shaft so that the members of said timber Whose ends are received in said niches extend angularly inwardly and upwardly with respect to the side walls of the shaft when the timber is in place therein, the pivotal connection of adjacent members including a pivot pin mounted in one of the members and received in an enlarged opening in the other of the members, and complementary surfaces on each of said members adjacent the pivotal connection therebetween adapted to interengage when the load of the roof of said shaft is applied to said timber, the said interengagement occurring before the pivot pin engages the side wall of the cooperating enlarged opening so that the said load is transmitted to the side walls of the shaft through the said complementary surfaces with substantially none of the load being transmitted through the pivot pin.

2. A mine timber as defined in claim 1 and in which the said complementary surfaces are arcuate whereby variations in the angularity between said members does not interfere with the interengagement of said surfaces for the transmission of load therethrough.

3. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft,,a pair of spaced members the lower ends of which are adapted to be respectively received in niches formed in the opposite side walls of the shaft, means loosely pivotally connecting the other ends of said pair of members to said first-mentioned member adjacent opposite ends of the latter, the said pivotal connections being so located that the said pair of members extend angularly inwardly and upwardly with respect to the side walls of the shaft when the timber is in place therein, and complementary surfaces on each of said members adjacent their pivotal connections adapted to interengage when the load of the roof of the shaft is applied to said firstmentioned member and effect transmission of that load to said pair of members thereby substantially relieving the pivotal connections of said load.

4. A mine timber as defined in claim 3 and in which the said complementary surfaces are arouate whereby variations in the angularity between said members does not interfere with the interengagement of said surfaces for the transmission of load therethrough.

5. A mine timber as defined in claim 3 and further comprising means carried by said first-mentioned member and verticall adjustable relative thereto to effect engagement with the roof of the shaft in which the timber is positioned and to transmit at least a part of the load of the latter to said timber.

6. A mine timber as defined in claim 3 and further comprising a jack screw cooperating with a threaded opening in the first-mentioned member intermediate the ends of the latter, the said jack screw having its axis substantially vertical when the timber is in place in a mine shaft and being adjustable relative to-the first-mentioned member to effect engagement with the roof of the shaft and transmit at least a part of the load of the latter to said timber.

'7. A mine timber as defined in claim 3 and in which at least one of said pair of members includes means for adjusting the length thereof.

8. A mine timber as defined in claim 3 and further comprising means for varying the lengths of said pair of members.

9. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft, a pair of spaced members the lower ends of which are adapted to be received in niches formed in the opposite side walls of the shaft, means loosely pivotally connecting the other ends of said pair of members to said first-mentioned member adjacent opposite ends of the latter, the combined length of said members being greater thanvthe width of the shaft and the distance between the pivotal connections being less than the width of the shaft so that the said pair of members extend angularly inwardly and upwardly with respect to the side walls of the shaft when the timber is in place therein, and complementary surfaces on each of said members adjacent their pivotal connections adapted to interengage when the load of the roof of the shaft is applied to said first-mentioned member and to effect transmission of that load to said pair of members thereby substantially relieving the pivotal connections of said load.

10. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft, a pair of spaced members the lower ends of which are adapted to be received in niches formed in the opposite side walls of the shaft, means loosely pivotall connecting the other ends of said pair of members to said first-mentioned member adjacent opposite ends of the latter, the said means each including a pivot pin mounted in one of said members and received in an enlarged opening in the adjacent member, the said pivotal connections being so located that the said pair of members extend angularly upwardly and inwardly with respect to the side walls of the shaft when the timber is in place therein, and complementary surfaces on each of said members adjacent their pivotal connections adapted to interengage when the load of the roof of said shaft is'applied tothe first-mentioned member, the said interengagement occurring before the corresponding pivot pin engages the side wall of the cooperating enlarged opening so that the said load is transmitted from the first-mentioned member through the complementary surfaces and the said pair of members to the side walls of the shaft and substantially none of the load is transmitted through the said pivot pins.

11. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft, a pair of spaced members the lower ends of which are adapted to be received in niches formed in the opposite side walls of the shaft, means loosely pivotally connecting the other ends of said pair of members to said first-mentioned member adjacent opposite ends of the latter, the combined lengths of said members being greater than the width of the shaft and the distance between the pivotal connections being less than the width of the shaft so that the said pair of members extend angularly upwardly and inwardly with respect to the side walls of the shaft when the timber is in place therein, the said means each including a pivot pin mounted in one of said members and received in an enlarged opening in the adjacent member, and complementary surfaces on each of said members adjacent their pivotal connections adapted to interengage when the load of the roof of said shaft is applied to the first-mentioned member, the said interengagement occurring before the corresponding pivot pin engages the side wall of the cooperating enlarged openin so that the said load is transmitted from the first-mentioned member through the complementary surfaces and the said pair of members to the side walls of the shaft and substantially none of the load is transmitted through the said pivot pins.

12. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft, a pair of spaced members the lower ends of which are adapted to be respectively received in niches formed in the opposite side walls of the shaft, means loosely pivotally connecting the other ends of said pair of members to said first-mentioned member adjacent opposite ends of the latter, means to adjust the over-all length of said timber, the said pivotal connections being so located and the length of said timber being so adjusted that the said pair of members extend angularly inwardly and upwardly with respect to the side walls of the shaft when the timber is in place therein, and complementary surfaces on each of said members adjacent their pivotal connections adapted to interengage when the load of the roof of the shaft is applied to said firstmentioned member and effect transmission of that load to said pair of members thereby substantially relieving the pivotal connections of said load. 7

13. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a first member adapted to extend substantially parallel with the roof of said shaft, the said member having a pair of spaced elongated longitudinally extending openings therein with each opening having spaced recesses extending obliquely therefrom, a pair of spaced members the lower ends of which are adapted to be respectively received in niches formed in the opposite walls of the shaft, a separate pivot pin carried by the other end of each of said pair of members with each pivot pin received in one of the slots of said first-mentioned member and adapted to selectively enter the said recesses so that the said pair of members extend angularly inwardly and upwardly with respect to the side walls of the shaft when the timber is in place therein, the first-mentioned member having surfaces adjacent each of said recesses which are complementary with surfaces provided on the said other ends of said pair of members, the said complementary surfaces being adapted to interengage before the said pivot pins have contacted the ends of said recesses whereby the load of the roof of said shaft is transmitted through said complementary surfaces and said pair of members to the side walls of said shaft.

14. A mine timber adapted to be positioned in a mine shaft to transmit the load of the roof to the side walls thereof, the said timber comprising a pair of members loosely pivotally connected together with the free ends of said timber being adapted to be received in niches in the opposite side walls of the shaft, the over-all length of said timber being greater than the width of the shaft so that the said members extend angularly inwardly and upwardly with respect to the side walls of the" shaft when the timber is in place therein, the pivotal connection of said members including a pivot pin mounted in one of the members and received in an enlarged opening in the other of the members, and

' complementary surfaces on said members adjacent their pivotal connection adapted to interengage when the load of the roof of said shaft is applied to said timber, the said interengagement occurring before the pivot pin engage the side wall of the enlarged opening so that the said load is transmitted to the side walls of the shaft through the said complementary surfaces with substantially none of the load being transmitted through the pivot pin.

15. A mine timber as defined in claim 14 and further comprising means on each of said members adapted to provide a seat for the lower end of a thrust member interposed between a member of the timber and the roof of said shaft.

MONROE J. MECHLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

